bug#13864: 24.3.50; emacsclient -t loops when connected to emacs server running in X11

[ashish.is@lostca.se (Ashish SHUKLA)]

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Hi Eli,

Sorry for the delay in follow-up.

On Fri, 08 Mar 2013 17:58:47 +0200, Eli Zaretskii <eliz@gnu.org> said:
>> From: ashish.is@lostca.se (Ashish SHUKLA)
>> Cc: 13864@debbugs.gnu.org
>> Date: Fri, 08 Mar 2013 15:38:30 +0530
>> 
>> >   (gdb) break dispnew.c:4509
>> >   (gdb) commands
>> >> p i
>> >> p desired_matrix->nrows
>> >> if i < desired_matrix->nrows
>> >> pgrowx desired_matrix->rows+i
>> >> end
>> 
>> I later added a 'continue' in here as Breakpoint 6 in the output.

> Yes, sorry about that, I forgot.

>> Not sure if the attached gdb output is any useful.

> It is, thanks.  I think we are making progress.

>> - emacs -Q 
>> - M-x server-start
>> - gdb stuff, breakpoints + loading .gdbinit
>> - Started an xterm of dimensions (maybe 20-25 rows)
>> - emacsclient -t
>> - key presses (none of them is C-x C-f)

> Emacs would begin to flicker after these, right?

No, it only starts flickering after I focus to X11 window and focus back to
emacsclient xterm window. Apologies, if I wasn't clear before in my
observations.

>> - Breakpoint 1 being hit and requiring me to type 'cont' on every hit
>> - After some 'cont' inputs, I deleted it, and re-added it as Breakpoint 6 with
>> 'continue' as mentioned above.
>> - Breakpoint 6 being continuously hit

> So you are saying that scrolling_1 is never called, is that right?

Right.

>> - C-x 5 0 in emacsclient window
>> - appended '====EMACSCLIENT STOPPED====' to logfile
>> - emacsclient -t
>> - Breakpoint 6 being hit
>> - I resized window to 4-5 rows in an effort to reduce no. of redraw messages
>> - Killed gdb after 2 minutes, which killed emacs.

> To have a way of terminating the session in a more civilized way, I
> frequently use the following trick: put a breakpoint at Fredraw_display,
> before you start the debugging session.  Then, whenever you want to
> change something or finish the session, just "M-x redraw-display RET"
> and GDB kicks in.

>> Let me know if you need more information.

> Hmm...  Some observations:

>   . update_frame_1 is constantly called with either the entire frame,
>     starting with the menu bar, or just with the last line of the
>     frame, which is the echo area.

>   . I see tooltip messages being displayed in the echo area.  You have
>     a mouse active (as far as Emacs is concerned) on the xterm frame,
>     is that right?  Can you disable it and see if the flickering
>     persists?

I don't know what you meant by mouse active. FTR, I don't use
"xterm-mouse-mode" in my .emacs.d/init.el nor the -Q config has that, if
that's what you're implying. Emacs instance in xterm doesn't have any effect
of mouse in it. The tooltip is courtesy some spurious key-presses during
debugging..

>   . There are some instances where Emacs displayed "Quit" in the echo
>     area.  Did you type C-g or some such?

Right, I did type that.

> Moving on in the investigation of the problem (assuming that
> disabling the mouse doesn't fix it), I assume that the function
> update_frame_line is being called to redraw the xterm frame, given the
> evidence you gathered this far.  First, let's make sure this is indeed
> so.  Use this breakpoint:

>   (gdb) break update_frame_line
>   (gdb) commands
>> p vpos
>> continue
>> end
>   (gdb)

> Please see if you see all the line numbers when you recreate the
> situation with flickering.

Yes, I saw them, the output is in "gdb-1.txt" attachment. The GDB output has
inline comments prefixed with '===='.

> If you indeed see all the line numbers of a frame, next thing is to
> find out whether on your system the FRAME_CHAR_INS_DEL_OK macro
> returns zero or non-zero.  (Depending on that, Emacs uses two separate
> portions of code in update_frame_line which try to avoid redrawing the
> parts of screen that didn't change.)  You could, for example, put a
> breakpoint inside this block:

>   if (!FRAME_CHAR_INS_DEL_OK (f))
>     {
>       int i, j;

>       /* Find the first glyph in desired row that doesn't agree with
> 	 a glyph in the current row, and write the rest from there on.  */
>       for (i = 0; i < nlen; i++)
> 	{
> 	  if (i >= olen || !GLYPH_EQUAL_P (nbody + i, obody + i))
> 	    {
> 	      /* Find the end of the run of different glyphs.  */
> 	      j = i + 1;
> 	      while (j < nlen
> 		     && (j >= olen
> 			 || !GLYPH_EQUAL_P (nbody + j, obody + j)
> 			 || CHAR_GLYPH_PADDING_P (nbody[j])))
> 		++j;

> 	      /* Output this run of non-matching chars.  */
> 	      cursor_to (f, vpos, i);
> 	      write_glyphs (f, nbody + i, j - i);
> 	      i = j - 1;

> 	      /* Now find the next non-match.  */
> 	    }
> 	}

>       /* Clear the rest of the line, or the non-clear part of it.  */
>       if (olen > nlen)
> 	{
> 	  cursor_to (f, vpos, nlen);
> 	  clear_end_of_line (f, olen);
> 	}

>       /* Make current row = desired row.  */
>       make_current (desired_matrix, current_matrix, vpos);
>       return;  <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
>     }

> on the marked line, and see if it ever breaks.

This output is in "gdb-2.txt" with inline comments.

The comments are added with: echo '==== $MESSAGE ====' >>gdb.txt
in a different xterm window.

FTR, I use Fluxbox 1.3.5 as my window manager, and running Xorg 7.5.2.

Let me know if you need anything else.

HTH
-- 
Ashish SHUKLA

“It is neccessary to have wished for death in order to know how good it is to
live.” ("Alexandre Dumas")

Sent from my Emacs

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